The present invention is related to a method of preparing an emulsion of a polyester resin having free carboxyl groups either pendant and/or terminal and an amino-functional silane. The emulsion is used alone or with other additives to function as a sizing composition for glass fibers. In the sizing composition the polyester resin functions as a film-former and the silane functions as a coupling agent.
In manufacturing glass fiber strands, a multitude of fine glass filaments are combined to yield the glass fiber strand. These fine glass filaments are formed by the rapid attenuation from molten cones of glass at the tips of small orifices in a bushing, for example, as in the operation shown in U.S. Pat. No. 2,133,238. In order to protect the glass filaments from interfilament abrasion, the filaments are coated during their formation with a sizing composition to protect the glass fiber strand against handling equipment during further processing and to give the glass fiber strand integrity and workability for any standard textile or reinforcement use. After the filaments have been treated with the sizing composition and gathered together into a strand the glass fiber strand is wound around a rapidly rotating drum to form a package.
Sizing compositions for use in treating glass fibers usually contain a lubricant, which provides the protection for the glass fiber strand; a film-former or binder that gives the glass fiber strand integrity and workability; a coupling agent that provides better adhesion between the glass fiber strand and the polymeric materials that are reinforced with the glass fiber strand; and other additives. The lubricant assists in imparting wet-out and allowing good contact between the polymeric material that is to be reinforced with the glass fibers and the glass fibers. The film-former should be water soluble or water emulsifiable and must be non-sensitive to water after curing. The art has developed a number of film-formers for use with different polymeric materials that are to be reinforced with glass fibers. Examples of these film-formers include polyesters, polyvinyl pyrrolidones, epoxy resins, polyamides, polyacrylates, polyvinyl alcohols, starches and the like. The coupling agent can be a Werner complex compound or an organo-silicon compound. Usually the coupling agent is a silane coupling agent that has a hydrolyzable moiety for bonding to the glass and an organic reactive moiety that is compatible with the polymeric material that is to be reinforced with the glass fibers. The lubricant, film-former, and coupling agent can be a single compound or a mixture of two or more compounds. One recognized problem of the use of organo silane compounds as coupling agents in sizing compositions is their tendency to rapidly hydrolyze in aqueous media to form their corresponding silanols and siloxanes. The rapid hydrolysis of the silane in a sizing composition which contains a film-former can lead to the coagulation and precipitation or settling out of the film-former or hydrolyzed silane or both.
One solution to this problem was proposed in U.S. Pat. No. 3,922,466 (Bell et al) wherein the silane coupling agent was prepared by reaction of a mercapto silane with a carboxylic acid anhydride whereby the mercapto group added across the double bond of the anhydride. The reaction is carried out in the presence of an amino catalyst and the resultant silane coupling agent is formulated into a glass fiber sizing composition usually containing a polyester resin and water. The silane coupling agent prepared in this manner reacts with water in the size to form the corresponding diacid which is further hydrolyzed in the size to form the corresponding silanols and polysiloxanes.
It has recently been suggested by the art to utilize a polyester resin having pendant carboxyl groups alone or in addition to other polyester resins in a sizing composition for treating glass fibers. The presence of the pendant carboxyl groups make the polyester resin more water soluble or dispersible in the sizing composition and provides a glass fiber strand with good wet-out properties. The presence of the excess carboxyl functionality of the polyester resin necessitates care in synthesis in order to avoid crosslinking by condensation. Typically in sizing compositions one or more silane coupling agents are used. A silane coupling agent that has been used to promote adhesion between the glass and the polymeric materials for which the glass fibers are used as reinforcement has been an amino functional silane. It is known in the art that amino functional silanes have a tendency to hydrolyze more rapidly than other types of silanes. Conventionally silane coupling agents are usually added to a sizing composition in an aqueous medium in order to facilitate hydrolysis so that the silanes are in the proper chemical form to attach to the glass fibers. When the amino silane is added in the conventional manner, i.e. after complete hydrolysis in an aqueous medium, to a sizing composition containing a polyester resin with pendant carboxyl groups the resultant sizing composition has a stability problem. The sizing composition is not stable for long periods of time because a portion of the sizing composition coagulates and eventually settles out.
It is an object of the present invention to provide a method of producing a more stable sizing composition that contains a polyester resin having free carboxyl groups either pendant and/or terminal and an amino silane.
It is a further object of the present invention to provide a sizing composition that contains a single component to perform the function of the film-former and the coupling agent.
An additional object of the present invention is to provide a method for making a sizing composition and a sizing composition wherein the coupling agent is more efficiently used.
It is a further additional object of the present invention to provide a method of preparing a composition and the composition wherein the formation of dimer polymers of the coupling agent is inhibited.
A further additional object of the present invention is to provide a method of producing a sizing composition wherein the coupling agent has been controllably hydrolyzed.